This invention relates in general to transport apparatus for transferring discrete objects from one location to another with a high degree of accuracy. More specifically, it relates to a high speed, vacuum pick and place mechanism suitable for shuttling a succession of integrated circuits (IC's) to a well-defined position in a test plane offset from a main device flow path.
In the manufacture of IC's and the like it is important to test each circuit reliably and at a high throughput rate. Typically modern IC testers operate at rates in excess of 5,000 IC's per hour with each IC being tested in an interval of approximately 100 milliseconds. The IC's are generally stored and move in an end-to-end linear array.
These devices must move the IC's from this columnar array, one at a time, to a test site where they can be momentarily placed into electrical connection with a test circuit through a contactor assembly which acts as an electrical interface. The alignment problems are critical since the quality of the test depends on each lead making a good electrical connection with a single associated contact of the contactor assembly. In the testing of IC devices having a surface mount configuration (typically a square plastic body with leads on four sides and termed herein "SMD"), the handling problems have been accentuated by the presence of soft, readily-deformed leads on all four sides of a device (as opposed to earlier dual-in-line (DIP) packaged IC's with only two parallel rows of leads). It is also essential to a successful test handler that the operation of this transport be reliable, exhibit good wear characteristics, and accommodate IC's of different dimensions and configurations.
Conventional SMD IC testers typically allow the IC to drop under the influence of gravity to a test site level. The device is then advanced by one or more plungers to a test plane where the IC connects to a contactor assembly. Final positioning of the device is accomplished by camming the device using tapered side walls.
With this arrangement the camming surfaces apply side forces to the device which for at least some products, e.g. PCC packaged devices, can cause the bending of leads. Side wall camming can also result in a transfer of conductive material from the leads to the cam surfaces which in turn can develop into leakage paths that degrade the testing. Another problem with a "closed" system established by the tapered side walls is that the side walls and the devices must meet close dimensional tolerances to produce the desired steering of the device while avoiding lead damage or a jamming of the device. Stated in other words, this approach is not tolerant of variations in the dimensions of the product. This system is also intolerant of error in positioning the device at the test site. An incorrectly positioned device can damage the device or the machine when it is driven by the plunger or plungers.
Horizontal pick and place systems are known, principally in Japan, for testing quad surface mount IC's. These test devices use a convention pick and place system where a picker raises a device, moves it horizontally to a position over a test site, lowers it, and then returns to pick up another device. In end result the device moves in a horizontal plane. At the test site four separately actuated mechanisms then clamp the leads to contacts. Another mechanism then removes the device from the test site after it is tested. This arrangement is comparatively mechanically complex, relatively slow, and it is not readily adapted to a variety of package configurations and dimensions.
It is therefore a principal object of this invention to provide a mechanism for reliably and rapidly transporting a succession of IC's, particularly SMD IC's, that provides a reliable alignment with a contractor and which substantially eliminates physical contact with the leads which could deform them.
Another principal object is to provide a transport mechanism with the foregoing advantages that readily accommodates IC's of varying dimensions and configurations.
A further object is to provide a transport mechanism with the foregoing advantages which does not require critical tolerances on steering surfaces and which is substantially less prone to jamming of the devices than prior art mechanisms.
Another object is to provide a transport mechanism which both shuttles devices to a test site and places them in electrical connection with a test circuit without additional clamping mechanisms.
A still further object is to provide a transport mechanism with the foregoing advantages which does not create current leakage paths near the test area through the transfer of conductive material from the leads to guide surfaces.